The present invention relates to an electrical power supply for momentarily supplying a DC high voltage to a load, and a fusing apparatus and a recording apparatus which employ such an electrical power supply.
In an electrophotographic flash fusing apparatus or the like, a DC high-voltage is produced from a low-voltage AC power supply, and the produced DC high voltage is used as a power supply for flash. In the prior art of an electrical power supply having such a purpose, a low voltage has been converted into a DC high voltage by using a Cockcroft circuit (alias "Cockcroft-Walton circuit"), as described in "High Voltage Engineering" pp. 90-91 (published by the Institute of Electrical Engineers of Japan) and JP-A-57-52380.
FIG. 10 is a circuit diagram of a conventional electrical power supply. A Cockcroft-Walton circuit 1 is constituted by rectifier elements, capacitors and resistors so as to produce a DC high voltage from an AC low voltage of a low-voltage AC power supply 11 and so as to charge a charging/discharging capacitor 23 with the produced DC high voltage through a limiting resistor 24. During the period of charging, a switch 8 is in an opened state, and upon completion of sufficient charging, the switch 8 is closed so that the capacitor 23 is momentarily discharged through a load 12. The limiting resistor 24 serves to prevent the rectifier elements of the Cockcroft-Walton circuit 1 from being damaged in the period of discharging.
In the above-mentioned prior art, there has been a problem that the electrical power supply is large in volume as well as in weight because of the presence of a charging/discharging capacitor and a limiting resistor, and there has been a further problem that the electrical power loss in the limiting resistor is equal to the power consumption in the load. Such problems have been serious particularly in an electrophotographic flash fusing apparatus and an electrophotographic flash pre-heating apparatus which have been required to be compact in size and low in power consumption.